In the present-day environmentally conscious world it is becoming increasingly important to ensure that polluting contaminants are not spilled onto or leaked into the soil. Apart from such contamination having a detrimental effect on any life directly supported by such contaminated soil, the very real danger exists that such contaminants leach from the contaminated soil into the water table or are washed into rivers or water storage areas, with further detrimental effects.
Unfortunately, the need for maintaining a contaminant-free soil has only been considered a priority in recent years. As a result, a large number of sites exist, both nationally and internationally, where the soil has been contaminated extensively with pollutants such as chemicals, hydrocarbons and/or other volatile organic pollutants. Furthermore, even with the best storage and transportation facilities available, pollution of soil still occurs during unintentional and accidental leakage and spillage of pollutants. Accordingly, there is a pressing need for a cost-effective method of removing pollutants.
A variety of approaches have been tried for removal of hydrocarbons, among them use of microbes (bioremediation), leaching, displacement aeration, and in situ forced air or induced air (evacuation) processes.
U.S. Pat. No. 5,035,537 of Rose shows a leaching process for removing contaminants from a layer of soil which is spread in a thin layer on an impervious base by treating the layer with an emulsification agent sprayed thereon which seeps down through the layer and is collected at the base. If any gases result from the leaching process, these are collected by a tent supported above the layer on stakes, and vented through an open flame burner which exhausts to atmosphere.
U.S. Pat. No. 5,011,329 of Nelson, et al. shows an in situ soil decontamination process in which hot gas is forced into cased boreholes drilled into or below a contaminated zone. The hot gas is forced up from the bottom of the borehole up through the in situ soil and is trapped and collected in a system of trenches emplaced under a gas impervious sheet on the surface of the soil. Contaminants entrained in the collected gas are burnt off in a burner which heats the gas that is forced into the boreholes.
U.S. Pat. No. 4,982,788 of Donnelly is another in situ process of drilling a plurality of boreholes into contaminated soil. Heated air is forced into a first set of wells to percolate laterally from the bottom of the wells to a second set of exhaust wells. Extrained contaminants are condensed above ground.
U.S. Pat. No. 4,867,064 of Bell shows a system for monitoring toxic waste leachate in a landfill comprising a plurality of interconnected, horizontally laid, perforated PVC or ABS collector pipes and a plurality of vertically oriented monitoring pipes in communication with the collector pipes. Levels and concentrations of toxic waste can be monitored at different points via the monitoring pipes. The pipe network is laid down before the fill is deposited.
U.S. Pat. No. 4,849,360 of Norris et al. shows a process of aerobically biodegrading contaminants in a mass of particulate solids in a sealed container. Gas containing oxygen is pumped into the container mass through at least two different levels of gas inlet conduits, with the correct oxygen content being maintained in the mass to sustain biodegrading micro-organisms to which a microbial nutrient (Restore 375) is added. The sealed container can be an excavation or pit lined with an impermeable liner.
U.S. Pat. No. 4,745,850 of Bastian et al. shows a wind-driven suction-type venting system for driving air through permeable conduits in contaminated soil. Contaminants flow into the conduits under action of gravity and are vented to atmosphere with the air driven through the conduits.
U.S. Pat. No. 4,842,448 of Koerner et al. is directed to an in situ vacuum method of removing organic solvents and hydrocarbons from the soil. To enhance the vacuum removal of contaminants, a liberating fluid such as heated air or steam may be pumped into the soil via angled conduits extending into the soil below the projected area of contamination.
The above-described in situ forced air and suction methods have the disadvantage that a substantial vacuum suction or forced air pressure is required to draw or force the contaminants and any liberating fluid that may be used out of the soil. This is because the soil mass is in situ. As a result of natural compaction of in situ soil, the spaces between the various particles of the soil are very small. Furthermore it is extremely difficult, with this method, to isolate the surface of the body of the soil which is exposed to atmosphere so that it is sealed well enough to have an efficient suction that does not draw air from the atmosphere or let forced air escape.
The present invention overcomes these disadvantages by removing the soil from its in situ position, thereby causing it to loosen with resultant larger voids between the soil particles for more efficient and more complete removal of hydrocarbons. In addition, this invention provides for a positive pressure combined with a negative pressure to enhance the removal of the contaminants from the soil.